/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.http.server.reactive;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Supplier;
import java.util.stream.Collectors;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseCookie;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;

/**
 * Base class for {@link ServerHttpResponse} implementations.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @author Sebastien Deleuze
 * @since 5.0
 */
public abstract class AbstractServerHttpResponse implements ServerHttpResponse {

    /**
     * COMMITTING -> COMMITTED is the period after doCommit is called but before
     * the response status and headers have been applied to the underlying
     * response during which time pre-commit actions can still make changes to
     * the response status and headers.
     */
    private enum State {NEW, COMMITTING, COMMITTED}


    private final Log logger = LogFactory.getLog(getClass());

    private final DataBufferFactory dataBufferFactory;

    @Nullable
    private Integer statusCode;

    private final HttpHeaders headers;

    private final MultiValueMap<String, ResponseCookie> cookies;

    private final AtomicReference<State> state = new AtomicReference<>(State.NEW);

    private final List<Supplier<? extends Mono<Void>>> commitActions = new ArrayList<>(4);


    public AbstractServerHttpResponse(DataBufferFactory dataBufferFactory) {
        Assert.notNull(dataBufferFactory, "DataBufferFactory must not be null");
        this.dataBufferFactory = dataBufferFactory;
        this.headers = new HttpHeaders();
        this.cookies = new LinkedMultiValueMap<>();
    }


    @Override
    public final DataBufferFactory bufferFactory() {
        return this.dataBufferFactory;
    }

    @Override
    public boolean setStatusCode(@Nullable HttpStatus statusCode) {
        if (this.state.get() == State.COMMITTED) {
            if (logger.isTraceEnabled()) {
                logger.trace("HTTP response already committed. " +
                        "Status not set to " + (statusCode != null ? statusCode.toString() : "null"));
            }
            return false;
        } else {
            this.statusCode = (statusCode != null ? statusCode.value() : null);
            return true;
        }
    }

    @Override
    @Nullable
    public HttpStatus getStatusCode() {
        return (this.statusCode != null ? HttpStatus.resolve(this.statusCode) : null);
    }

    /**
     * Set the HTTP status code of the response.
     *
     * @param statusCode the HTTP status as an integer value
     * @since 5.0.1
     */
    public void setStatusCodeValue(@Nullable Integer statusCode) {
        this.statusCode = statusCode;
    }

    /**
     * Return the HTTP status code of the response.
     *
     * @return the HTTP status as an integer value
     * @since 5.0.1
     */
    @Nullable
    public Integer getStatusCodeValue() {
        return this.statusCode;
    }

    @Override
    public HttpHeaders getHeaders() {
        return (this.state.get() == State.COMMITTED ?
                HttpHeaders.readOnlyHttpHeaders(this.headers) : this.headers);
    }

    @Override
    public MultiValueMap<String, ResponseCookie> getCookies() {
        return (this.state.get() == State.COMMITTED ?
                CollectionUtils.unmodifiableMultiValueMap(this.cookies) : this.cookies);
    }

    @Override
    public void addCookie(ResponseCookie cookie) {
        Assert.notNull(cookie, "ResponseCookie must not be null");

        if (this.state.get() == State.COMMITTED) {
            throw new IllegalStateException("Can't add the cookie " + cookie +
                    "because the HTTP response has already been committed");
        } else {
            getCookies().add(cookie.getName(), cookie);
        }
    }

    /**
     * Return the underlying server response.
     * <p><strong>Note:</strong> This is exposed mainly for internal framework
     * use such as WebSocket upgrades in the spring-webflux module.
     */
    public abstract <T> T getNativeResponse();


    @Override
    public void beforeCommit(Supplier<? extends Mono<Void>> action) {
        this.commitActions.add(action);
    }

    @Override
    public boolean isCommitted() {
        return this.state.get() != State.NEW;
    }

    @Override
    public final Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
        return new ChannelSendOperator<>(body,
                writePublisher -> doCommit(() -> writeWithInternal(writePublisher)));
    }

    @Override
    public final Mono<Void> writeAndFlushWith(Publisher<? extends Publisher<? extends DataBuffer>> body) {
        return new ChannelSendOperator<>(body,
                writePublisher -> doCommit(() -> writeAndFlushWithInternal(writePublisher)));
    }

    @Override
    public Mono<Void> setComplete() {
        return !isCommitted() ? doCommit(null) : Mono.empty();
    }

    /**
     * A variant of {@link #doCommit(Supplier)} for a response without no body.
     *
     * @return a completion publisher
     */
    protected Mono<Void> doCommit() {
        return doCommit(null);
    }

    /**
     * Apply {@link #beforeCommit(Supplier) beforeCommit} actions, apply the
     * response status and headers/cookies, and write the response body.
     *
     * @param writeAction the action to write the response body (may be {@code null})
     * @return a completion publisher
     */
    protected Mono<Void> doCommit(@Nullable Supplier<? extends Mono<Void>> writeAction) {
        if (!this.state.compareAndSet(State.NEW, State.COMMITTING)) {
            if (logger.isDebugEnabled()) {
                logger.debug("Skipping doCommit (response already committed).");
            }
            return Mono.empty();
        }

        this.commitActions.add(() -> {
            applyStatusCode();
            applyHeaders();
            applyCookies();
            this.state.set(State.COMMITTED);
            return Mono.empty();
        });

        if (writeAction != null) {
            this.commitActions.add(writeAction);
        }

        List<? extends Mono<Void>> actions = this.commitActions.stream()
                .map(Supplier::get).collect(Collectors.toList());

        return Flux.concat(actions).next();
    }


    /**
     * Write to the underlying the response.
     *
     * @param body the publisher to write with
     */
    protected abstract Mono<Void> writeWithInternal(Publisher<? extends DataBuffer> body);

    /**
     * Write to the underlying the response, and flush after each {@code Publisher<DataBuffer>}.
     *
     * @param body the publisher to write and flush with
     */
    protected abstract Mono<Void> writeAndFlushWithInternal(Publisher<? extends Publisher<? extends DataBuffer>> body);

    /**
     * Write the status code to the underlying response.
     * This method is called once only.
     */
    protected abstract void applyStatusCode();

    /**
     * Apply header changes from {@link #getHeaders()} to the underlying response.
     * This method is called once only.
     */
    protected abstract void applyHeaders();

    /**
     * Add cookies from {@link #getHeaders()} to the underlying response.
     * This method is called once only.
     */
    protected abstract void applyCookies();

}
